Density of information recorded on a magnetic recording medium has been increasing at a remarkable pace in recent years. It is a common practice to use a magnetic head for recording and reproducing information, the magnetic head having a slider that runs while being lifted over a recording medium, the slider being provided with an electromagnetic converter element.
The slider used in the magnetic head is required to be high in machinability and in wear resistance, and its surface which opposes the recording medium and experiences a force by air when the slider is floating in air is required to be very smooth. The slider is manufactured, for example, in the following procedure.
An insulating film made from amorphous alumina is formed by sputtering process on a ceramic substrate made from Al2O3—TiC ceramics or the like. A plurality of electromagnetic converter elements such as MR (magnetoresistance) element (hereinafter referred to as an MR element), GMR (giant magnetoresistance) element (hereinafter referred to as a GMR element), TMR (tunneling magnetoresistance) element (hereinafter referred to as a TMR element) or AMR (anisotropic magnetoresistance) element (hereinafter referred to as an AMR element), that uses magnetoresistance effect are mounted in a row at desired intervals on the insulating film.
The ceramic substrate bearing the plurality of electromagnetic converter elements disposed in a row is cut into rectangles by means of a slicing machine or a dicing saw. After polishing the cut surfaces of the rectangular ceramic substrate to be mirror-finished surfaces, part of the mirror-finished surface is removed by ion milling process or reactive ion etching process to thereby form a flow passage, while using the remaining mirror-finished surface as the floating surface. Then the rectangular ceramic substrate is divided into chips, so as to obtain the magnetic head having the slider provided with the electromagnetic converter elements.
The slider has, on the surface opposing the recording medium comprising a magnetic recording layer, the floating surface mirror-finished by polishing and the flow passage formed by removing a part of the mirror-finished surface, so that information is recorded and reproduced by the magnetic head lifted by a force generated by the recording medium rotating at a high speed not to touch the recording medium.
The recording medium drive unit (hard disk drive unit) having such a magnetic head as described above mounted therein is under ever increasing demand to have greater recording capacity with higher recording density. To meet these requirements, the magnetic head must be kept at a height as low as 10 nm or less above the hard disk. However, clearance of 10 nm or less between the hard disk rotating at a high speed and the magnetic head increases the possibility of the hard disk and the magnetic head touching each other due to vibration and impact, causing crystal grains of the compound that forms the slider constituting the magnetic head to come off (hereinafter referred to as grain fall-off), which may damage the hard disk and/or the magnetic disk and make it impossible to record and reproduce information. Crystal grains may also come off from the cut surface of the magnetic head substrate being divided into rectangular pieces and chips, or from the portion where the flow passage is formed by the ion milling process or reactive ion etching process, which may also cause the same trouble when falling onto the hard disk rotating at a high speed.
Accordingly, it is required to use a material that does not allow the crystal grains of the constituting compound to easily come off, for the magnetic head substrate used in forming the slider that constitutes the magnetic head, and it is necessary to improve the bonding between the crystal grains, namely to improve the sintering characteristic.
To meet these requirements, Patent Document 1 proposes Al2O3—TiC-based sintered body comprising 50 to 75% by weight of Al2O3 and 25 to 50% by weight of TiC as main components, and contains 0.03 to 0.5 parts by weight of sintering additive based on 100 parts by weight of the main components, wherein a mean crystal grain size in the sintered body is from 0.4 to 1.2 μm and standard deviation of the diameters of equivalent circles of the crystal grains is 0.35 or less. It is described that this sintered body has improved chipping resistance and high fracture toughness.
Patent Document 2 proposes a ceramic composite material containing fine TiC grains having a grain size of 2.0 μm or less, dispersed among crystal grains of Al2O3 matrix having a grain size of 0.5 μm to 100 μm.    Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 2000-103667    Patent Document 2: Japanese Patent No. 2,664,760